Selective catalytic reduction (scr) catalyst depletion control systems and methods

ABSTRACT

A dosing control system for a vehicle includes a current storage module, an adaption triggering module, and an adaption ending module. The current storage module estimates an amount of ammonia stored by a selective catalytic reduction (SCR) catalyst. The adaptation triggering module triggers a reduction of the amount of ammonia stored by the SCR catalyst to zero when a first amount of nitrogen oxides (NOx) measured by a first NOx sensor located downstream of the SCR catalyst is greater than a predicted value of the first amount of NOx. The adaptation ending module selectively ends the reduction and enables injection of dosing agent based on a comparison of the first amount of NOx with a second amount of NOx upstream of the SCR catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______(Attorney Docket No. P011881-PTUS-DPH), which was filed on [the same dayas the present application]. The disclosure of the above application isincorporated herein by reference in its entirety.

FIELD

The present disclosure relates to internal combustion engines and moreparticularly to exhaust treatment systems.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Air is drawn into an engine through an intake manifold. A throttle valvecontrols airflow into the engine. The air mixes with fuel from one ormore fuel injectors to form an air/fuel mixture. The air/fuel mixture iscombusted within one or more cylinders of the engine. Combustion of theair/fuel mixture generates torque.

Exhaust resulting from the combustion of the air/fuel mixture isexpelled from the cylinders to an exhaust system. The exhaust mayinclude particulate matter (PM) and gas. The exhaust gas includesnitrogen oxides (NOx), such as nitrogen oxide (NO) and nitrogen dioxide(NO₂). A treatment system reduces NOx and PM in the exhaust.

The exhaust flows from the engine to an oxidation catalyst (OC). The OCremoves hydrocarbons and/or carbon oxides from the exhaust. The exhaustflows from the OC to a selective catalytic reduction (SCR) catalyst. Adosing agent injector injects a dosing agent into the exhaust stream,upstream of the SCR catalyst. Ammonia (NH₃) provided by the dosing agentis absorbed by the SCR catalyst. Ammonia reacts with NOx in the exhaustpassing the SCR catalyst.

A dosing module controls the mass flow rate of dosing agent injected bythe dosing agent injector. In this manner, the dosing module controlsthe supply of ammonia to the SCR catalyst and the amount of ammoniastored by the SCR catalyst. The amount of ammonia stored by the SCRcatalyst is referred to as current storage (e.g., grams). The percentageof NOx input to the SCR catalyst that is removed from the exhaust isreferred to as the NOx conversion efficiency. The NOx conversionefficiency is related to the current storage of the SCR catalyst. Forexample, the NOx conversion efficiency increases as the current storageof the SCR catalyst increases and vice versa. The dosing module maycontrol the injection of dosing agent, for example, to maximize the NOxconversion efficiency.

SUMMARY

A dosing control system for a vehicle includes a current storage module,an adaption triggering module, and an adaption ending module. Thecurrent storage module estimates an amount of ammonia stored by aselective catalytic reduction (SCR) catalyst. The adaptation triggeringmodule triggers a reduction of the amount of ammonia stored by the SCRcatalyst to zero when a first amount of nitrogen oxides (NOx) measuredby a first NOx sensor located downstream of the SCR catalyst is greaterthan a predicted value of the first amount of NOx. The adaptation endingmodule selectively ends the reduction and enables injection of dosingagent based on a comparison of the first amount of NOx with a secondamount of NOx upstream of the SCR catalyst.

A dosing control system for a vehicle includes an adaption triggeringmodule, a dosing management module, and an adaption ending module. Theadaptation triggering module triggers an adaptation event when a firstamount of nitrogen oxides (NOx) measured by a first NOx sensor locateddownstream of a selective catalytic reduction (SCR) catalyst is greaterthan a predicted value of the first amount of NOx. The dosing managementmodule disables injection of dosing agent during the adaptation event.The adaptation ending module selectively ends the adaptation event basedon a comparison of the first amount of NOx with a second amount of NOxmeasured by a second NOx sensor located upstream of the SCR catalyst.

A dosing control method for a vehicle includes: estimating an amount ofammonia stored by a selective catalytic reduction (SCR) catalyst;triggering a reduction of the amount of ammonia stored by the SCRcatalyst to zero when a first amount of nitrogen oxides (NOx) measuredby a first NOx sensor located downstream of the SCR catalyst is greaterthan a predicted value of the first amount of NOx; and selectivelyending the reduction and enabling injection of dosing agent based on acomparison of the first amount of NOx with a second amount of NOxupstream of the SCR catalyst.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an exemplary engine systemaccording to the principles of the present disclosure;

FIG. 2 is a functional block diagram of an exemplary selective catalyticreduction (SCR) catalyst control system according to the principles ofthe present disclosure;

FIG. 3 includes an exemplary graph of input nitrogen oxides (NOx) as afunction of time, an exemplary graph of current storage as a function oftime, and an exemplary graph of output NOx as a function of timeaccording to the principles of the present disclosure;

FIGS. 4A-4B include exemplary graphs of NOx as a function of time whenthe SCR catalyst is underloaded according to the principles of thepresent disclosure;

FIGS. 5A-5B include exemplary graphs of NOx as a function of time whenthe SCR catalyst is overloaded according to the principles of thepresent disclosure; and

FIG. 6 is a flowchart depicting an exemplary method of performing anadaptation event according to the principles of the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the disclosure, its application, or uses. For purposesof clarity, the same reference numbers will be used in the drawings toidentify similar elements. As used herein, the phrase at least one of A,B, and C should be construed to mean a logical (A or B or C), using anon-exclusive logical or. It should be understood that steps within amethod may be executed in different order without altering theprinciples of the present disclosure.

As used herein, the term module may refer to, be part of, or include anApplication Specific Integrated Circuit (ASIC); an electronic circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor (shared, dedicated, or group) that executes code; othersuitable components that provide the described functionality; or acombination of some or all of the above, such as in a system-on-chip.The term module may include memory (shared, dedicated, or group) thatstores code executed by the processor.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared, as used above, means that some or allcode from multiple modules may be executed using a single (shared)processor. In addition, some or all code from multiple modules may bestored by a single (shared) memory. The term group, as used above, meansthat some or all code from a single module may be executed using a groupof processors. In addition, some or all code from a single module may bestored using a group of memories.

The apparatuses and methods described herein may be implemented by oneor more computer programs executed by one or more processors. Thecomputer programs include processor-executable instructions that arestored on a non-transitory tangible computer readable medium. Thecomputer programs may also include stored data. Non-limiting examples ofthe non-transitory tangible computer readable medium are nonvolatilememory, magnetic storage, and optical storage.

A dosing control module controls injection of a dosing agent (e.g.,urea) into an exhaust system upstream of a selective catalytic reduction(SCR) catalyst. The SCR catalyst receives exhaust output by an engine ofa vehicle. The exhaust includes nitrogen oxides (NOx). Ammonia (NH₃)provided to the SCR catalyst via the dosing agent reacts with NOx,thereby reducing the amount of NOx that is output from the SCR catalyst.

The dosing control module estimates an amount of ammonia stored by theSCR catalyst (current storage) and controls dosing agent injection basedon the current storage. The dosing control module predicts an amount ofNOx that will be measured by a NOx sensor located downstream of the SCRcatalyst (i.e., a downstream NOx sensor) based on the current storage.

The dosing control module initiates performance of an adaptation eventwhen the NOx measured by the downstream NOx sensor is greater than thepredicted NOx. When the measured NOx is different than the predictedNOx, the estimate of the current storage may have been greater than orless than an actual current storage of the SCR catalyst.

The dosing control module disables dosing agent injection during theadaptation event to deplete the SCR catalyst of ammonia. The dosingcontrol module of the present disclosure monitors the NOx measured bythe downstream NOx sensor and a NOx measured by a second NOx sensorlocated upstream of the SCR catalyst (i.e., an upstream NOx sensor) or amodeled value of the NOx upstream of the SCR catalyst during theadaptation event.

The dosing control module selectively ends the adaptation event based ona comparison of the NOx measurements. For example only, the dosingcontrol module selectively ends the adaptation event when a differencebetween the NOx measurements is less than a predetermined difference. Inthis manner, the dosing control module selectively ends the adaptationevent when the NOx measurements converge. Selectively ending theadaptation event based on the convergence of the NOx measurementsinstead of performing the adaptation event using a predetermined numberof phases may shorten the length (i.e., period) of the adaptation eventif the actual current storage of the SCR catalyst is less than estimatedcurrent storage at the time when the adaptation event is triggered.

Referring now to FIG. 1, a functional block diagram of an exemplaryengine system 100 is presented. An engine 102 generates drive torque fora vehicle. While the engine 102 is shown and will be discussed as adiesel type engine, the engine 102 may be another suitable type ofengine, such as a spark-combustion engine or another type of compressioncombustion engine. One or more electric motors (or motor-generators) mayadditionally generate drive torque.

Air is drawn into the engine 102 through an intake manifold 104. Airflowinto the engine 102 may be varied using a throttle valve 106. A throttleactuator module 108 controls opening of the throttle valve 106. One ormore fuel injectors, such as fuel injector 110, mix fuel with the air toform an air/fuel mixture. The air/fuel mixture is combusted withincylinders of the engine 102, such as cylinder 114. Although the engine102 is depicted as including one cylinder, the engine 102 may includemore than one cylinder.

Exhaust is expelled from the engine 102 to an exhaust system 120. Theexhaust may include particulate matter (PM) and exhaust gas. The exhaust(gas) includes nitrogen oxides (NOx), such as nitrogen oxide (NO) andnitrogen dioxide (NO₂). The exhaust system 120 includes a treatmentsystem that reduces the respective amounts of NOx and PM in the exhaust.

The exhaust system 120 includes an oxidation catalyst (OC) 122 and aselective catalytic reduction (SCR) catalyst 124. The exhaust system 120may also include a particulate filter (not shown). The exhaust flowsfrom the engine 102 to the OC 122. For example only, the OC 122 mayinclude a diesel oxidation catalyst (DOC). The exhaust flows from the OC122 to the SCR catalyst 124. The exhaust may flow from the SCR catalyst124 to the particulate filter. In various implementations, theparticulate filter may be implemented in a common housing with the SCRcatalyst 124. For example only, the particulate filter may include adiesel particulate filter (DPF).

A dosing agent injector 130 injects a dosing agent into the exhaustsystem 120 upstream of the SCR catalyst 124. For example only, thedosing agent injector 130 may inject the dosing agent at a locationbetween the OC 122 and the SCR catalyst 124. The dosing agent mayinclude urea (CO(NH₂)₂), ammonia (NH₃), and/or another suitable type ofdosing agent. The dosing agent may also be referred to as an emissionsfluid (EF) or a diesel emissions fluid (DEF). In implementations wherethe dosing agent includes urea, the urea reacts with the exhaust toproduce ammonia, and ammonia is supplied to the SCR catalyst 124. Thedosing agent may be diluted with water (H₂0) in various implementations.In implementations where the dosing agent is diluted with water, heat(e.g., from the exhaust) evaporates the water, and ammonia is suppliedto the SCR catalyst 124. An exemplary chemical equation that isillustrative of the production of ammonia from an exemplary dosing agentsolution is provided below.

HCNO+H₂O→NH₃+CO₂

The SCR catalyst 124 stores (i.e., absorbs) ammonia supplied by thedosing agent. For example only, the SCR catalyst 124 may include avanadium catalyst, a zeolite catalyst, and/or another suitable type ofSCR catalyst. An exemplary chemical equation that is illustrative ofammonia absorption is provided below.

NH₃+S→NH₃(S)

The SCR catalyst 124 catalyzes a reaction between stored ammonia and NOxpassing the SCR catalyst 124. The amount of ammonia stored by the SCRcatalyst 124 is referred to as current storage. The current storage maybe expressed as a mass of ammonia (e.g., grams), a number of moles ofammonia, or another suitable measure of the amount of ammonia stored bythe SCR catalyst 124.

NOx and ammonia react at a known rate, which may be referred to as areaction rate. The reaction rate may be described by the equation:

${RR} = \frac{X\mspace{14mu} {Moles}\mspace{14mu} {NH}_{3}}{1\mspace{14mu} {Moles}\mspace{14mu} {NOx}}$

where RR is the reaction rate and X varies depending on the amount ofnitrogen dioxide (NO₂) in the exhaust. For example only, X may varybetween from 1.0 and 1.333.

A percentage of NOx input to the SCR catalyst 124 that is removed fromthe exhaust via reaction with ammonia may be referred to as NOxconversion efficiency. The NOx conversion efficiency is directly relatedto the current storage of the SCR catalyst 124. For example only, theNOx conversion efficiency increases as the current storage of the SCRcatalyst 124 increases.

The current storage of the SCR catalyst 124, however, is limited to amaximum amount of ammonia. This maximum amount of ammonia is referred toas the maximum storage capacity of the SCR catalyst 124. Maintaining thecurrent storage of the SCR catalyst 124 near the maximum storagecapacity ensures that a maximum amount of NOx is removed from theexhaust. In other words, maintaining the current storage near themaximum storage capacity may ensure that a greatest possible NOxconversion efficiency is achieved.

However, maintaining the current storage at or near the maximum storagecapacity also increases the possibility that ammonia will be exhaustedfrom the exhaust system 120. Exhausting ammonia from the exhaust system120 may be referred to as ammonia slip. The increased possibility ofammonia slip may be attributable to the inverse relationship between themaximum storage capacity and the temperature of the SCR catalyst 124.More specifically, the maximum storage capacity decreases as the SCRtemperature increases, and the decrease in the maximum storage capacitymay cause ammonia to desorb (i.e., release) from the SCR catalyst 124.In other words, an increase in the SCR temperature causes a decrease inmaximum storage capacity, and ammonia stored in excess of this decreasedmaximum storage capacity may desorb from the SCR catalyst 124. Thus, anincrease in the SCR temperature may cause ammonia slip. An exemplarychemical equation that is illustrative of ammonia desorption is providedbelow.

NH₃(S)→NH₃+S

All or a portion of the ammonia supplied by the dosing agent may oxidizebefore or after being absorbed by the SCR catalyst 124. For example,ammonia may react with oxygen in the exhaust to produce nitrogen (N₂)and water (H₂O). Ammonia oxidation may be triggered by, for example,heat. Exemplary chemical equations that are illustrative of ammoniaoxidation are provided below.

4NH₃+3O₂→2N₂+6H₂O

2NH₃+2O₂→N₂O+3H₂O

4NH₃+5O₂→4NO+6H₂O

The reaction of ammonia with NOx produces nitrogen and water. Othercomponents of the exhaust, such as oxygen (O₂), may also be involved inthe ammonia and NOx reaction. The exemplary chemical equations providedbelow are illustrative of the reaction of ammonia and NOx.

4NH₃+4NO+O₂→4N₂+6H₂O

4NH₃+2NO+2NO₂→4N₂+6H₂O

8NH₃+6NO₂→7N₂+12H₂O

An upstream NOx sensor 142 measures NOx in the exhaust at a locationupstream of the OC 122. For example only, the upstream NOx sensor 142may measure a mass flowrate of NOx (e.g., grams per second), aconcentration of NOx (e.g., parts per million), or another suitablemeasure of the amount of NOx. The upstream NOx sensor 142 generates aninput NOx signal 158 based on the NOx in the exhaust upstream of the OC122. In various implementations, the upstream NOx sensor 142 may beomitted and the input NOx may be modeled based on one or more engineoperating parameters. A first temperature sensor 144 measurestemperature of the exhaust upstream of the OC 122. The first temperaturesensor 144 generates a first temperature signal 160 based on thetemperature of the exhaust upstream of the OC 122.

An oxygen sensor 146 measures oxygen (O₂) in the exhaust at a locationbetween the OC 122 and the SCR catalyst 124. The oxygen sensor 146generates an oxygen signal 162 based on the oxygen in the exhaustbetween the OC 122 and the SCR catalyst 124. A second temperature sensor148 measures temperature of the exhaust at a location between the OC 122and the SCR catalyst 124. The second temperature sensor 148 generates asecond temperature signal 164 based on the temperature of the exhaustbetween the OC 122 and the SCR catalyst 124. For example only, theoxygen sensor 146 and the second temperature sensor 148 may be locatedbetween where the dosing agent injector 130 injects the dosing agent andthe SCR catalyst 124.

A downstream NOx sensor 150 measures NOx in the exhaust at a locationdownstream of the SCR catalyst 124. For example only, the downstream NOxsensor 150 may measure a mass flowrate of NOx (e.g., grams per second),a concentration of NOx (e.g., parts per million), or another suitablemeasure of the amount of NOx. The downstream NOx sensor 150 generates anoutput NOx signal 166 based on the NOx in the exhaust downstream of theSCR catalyst 124. The downstream NOx sensor 150 is also cross-sensitiveto ammonia and, therefore, the output NOx signal may also reflectammonia in the exhaust downstream of the SCR catalyst 124. A thirdtemperature sensor 152 measures temperature of the exhaust downstream ofthe SCR catalyst 124. The third temperature sensor 152 generates a thirdtemperature signal 168 based on the temperature of the exhaustdownstream of the SCR catalyst 124.

One or more other sensors 156 may be implemented in the engine system100. For example only, the other sensors 156 may include a mass airflowrate (MAF) sensor, an exhaust flow rate (EFR) sensor, an intake airtemperature (IAT) sensor, a coolant temperature sensor, a manifoldabsolute pressure (MAP) sensor, an engine speed (RPM) sensor, an exhaustpressure sensor, and/or other suitable sensors.

An engine control module (ECM) 170 controls the torque output of theengine 102. The ECM 170 may include a dosing control module 190 thatcontrols the injection of the dosing agent. For example only, the dosingcontrol module 190 may control the timing and rate of dosing agentinjection. The dosing control module 190 controls the supply of ammoniato the SCR catalyst 124 and the current storage of the SCR catalyst 124via controlling the injection of dosing agent.

The rate at which dosing agent is injected may be referred to as adosing rate (e.g., grams per second), and the rate at which ammonia issupplied to the SCR catalyst 124 may be referred to as an ammonia supplyrate (e.g., grams per second). The dosing control module 190 maydetermine a target supply rate for supplying ammonia to the SCR catalyst124, determine a target dosing rate to achieve the target supply rate,and control the injection of dosing agent at the target dosing rate.

The dosing control module 190 predicts the amount of NOx that will bemeasured by the downstream NOx sensor 150 and compares the predictedamount of NOx with the amount of NOx measured by the downstream NOxsensor 150. The dosing control module 190 selectively initiatesperformance of an adaptation event based on the comparison of thepredicted amount of NOx with the amount of NOx measured by thedownstream NOx sensor 150. For example only, the dosing control module190 may trigger the performance of an adaptation event when the NOxmeasured by the downstream NOx sensor 150 is greater than the predictedamount of NOx. When the measured NOx is greater than the predictedamount of NOx, the current storage estimated by the dosing controlmodule 190 may be greater than or less than the actual amount of ammoniastored by the SCR catalyst 124.

An adaptation event involves disabling (or slowing) the injection ofdosing agent to deplete the SCR catalyst 124 of ammonia. The dosingcontrol module 190 determines a depleting amount of input NOx based onthe current storage when the adaptation event is triggered. The dosingcontrol module 190 monitors the input and output NOx measured by theupstream and downstream NOx sensors 142 and 150, respectively, duringthe adaptation event to determine when the SCR catalyst 124 is depletedof ammonia.

The dosing control module 190 selectively triggers an end of theadaptation event based on a comparison of the input and output NOxmeasurements. More specifically, the dosing control module 190selectively triggers the end of the adaptation event when a differencebetween the input and output NOx is less than a predetermineddifference. In other words, the dosing control module 190 selectivelytriggers the end of the adaptation event when the input and output NOxmeasurements are within a predetermined range of each other.

The dosing control module 190 also determines and tracks an accumulated(or total) amount of NOx input to the SCR catalyst 124 (accumulatedinput NOx) during the adaptation event. The dosing control module 190may determine whether the actual current storage of the SCR catalyst 124was greater than the estimated current storage (i.e., overloaded) orless than the estimated current storage (i.e., underloaded) based on acomparison of the accumulated input NOx with the depleting amount. Forexample only, the dosing control module 190 may determine that the SCRcatalyst 124 was overloaded when the accumulated input NOx is greaterthan the depleting amount. Conversely, the dosing control module 190 maydetermine that the SCR catalyst 124 was underloaded when the accumulatedinput NOx is less than the depleting amount.

The dosing control module 190 applies a dosing rate adjustment factor tothe target dosing rate. In other words, the dosing control module 190adjusts the target dosing rate based on the dosing rate adjustmentfactor. The dosing control module 190 may selectively increase ordecrease the dosing rate adjustment factor based on whether the SCRcatalyst 124 was overloaded or underloaded when the adaptation event wastriggered. More specifically, the dosing control module 190 increasesand decreases the dosing rate adjustment factor when the SCR catalyst124 was underloaded and overloaded, respectively, when the adaptationevent was triggered. In this manner, the dosing control module 190 mayincrease or decrease the target supply rate to prevent futureunderloading or overloading of the SCR catalyst 124 after the adaptationevent.

The dosing control module 190 may determine a magnitude of theadjustment for the dosing rate adjustment factor based on a differencebetween the accumulated input NOx and the depleting amount. For exampleonly, the magnitude of the adjustment to the dosing rate adjustmentfactor may increase as the difference increases. In this manner, thedosing control module 190 may variably adjust the dosing rate adjustmentfactor based on the extent to which the SCR catalyst 124 was overloadedor underloaded when the adaptation event was triggered.

Referring now to FIG. 2, a functional block diagram of an exemplarydosing control system 200 is presented. The dosing control module 190may include a dosing management module 202, an injector control module206, a percentage setting module 210, a current storage module 214, aconversion efficiency module 218, a predicted NOx output module 222, anda NO2 input module 226. The dosing control module 190 may also includean adaptation triggering module 240, an adaptation ending module 244, atimer module 248, an accumulation module 252, a condition assessmentmodule 256, a factor adjustment module 260, and a differencedetermination module 270.

The dosing management module 202 determines a target dosing rate 272.The dosing management module 202 adjusts the target dosing rate 272based on the dosing rate adjustment factor before providing the targetdosing rate 272 to the injector control module 206. For example only,the dosing rate adjustment factor 273 may be a value between 2.0 and0.0, inclusive. The dosing management module 202 may adjust the targetdosing rate 272 by adjusting (e.g., multiplying) the target dosing rate272 by the dosing rate adjustment factor 273 before providing the targetdosing rate 272 to the injector control module 206.

The injector control module 206 applies a signal 274 to the dosing agentinjector 130 to achieve the target dosing rate 272. The signal 274applied to the dosing agent injector 130 may be, for example, a pulsewidth modulation (PWM) signal or another suitable type of signal. Theinjector control module 206 may set the duty cycle (i.e., percentage oftime ON during a predetermined period of time) of the signal 274 toachieve the target dosing rate 272 and apply the PWM signal to thedosing agent injector 130.

The target dosing rate 272 corresponds to an injection rate of thedosing agent to achieve the target supply rate of ammonia to the SCRcatalyst 124. The target supply rate corresponds to a desired rate tosupply ammonia to the SCR catalyst 124. In implementations where ammoniais injected as the dosing agent, the target dosing rate 272 may be equalto or approximately equal to the target supply rate. The dosingmanagement module 202 may determine the target supply rate 272 based ona target current storage for the SCR catalyst 124, the current storage276 of the SCR catalyst 124, the input NOx 158, and/or one or more othersuitable parameters. The dosing management module 202 may determine thetarget supply rate, for example, to maximize the NOx conversionefficiency, to minimize the output NOx 166, to minimize ammonia slip,and/or to achieve one or more other suitable goals.

The dosing management module 202 may determine the target currentstorage based on a percentage of the maximum storage capacity of the SCRcatalyst 124. The maximum storage capacity may be determined based onthe SCR temperature 278. For example only, the maximum storage capacitydecreases as the SCR temperature 278 increases, and vice versa. Thepercentage setting module 210 may determine the percentage based on, forexample, the engine speed 280, engine load 282, and the SCR temperature278. The SCR temperature 278 may be estimated based on the first,second, and third temperatures 160, 164, and 168, respectively, invarious implementations. In other implementations, the SCR temperature278 may be measured using an SCR temperature sensor (not shown) ordetermined in another suitable manner. The SCR temperature 278 may be,for example, an average temperature of the SCR catalyst 124.

The current storage module 214 estimates the current storage 276 of theSCR catalyst 124. For example only, the current storage module 214 mayestimate the current storage 276 of the SCR catalyst 124 based on thetarget supply rate, the input NOx 158, the output NOx 166, and/or one ormore other suitable parameters. More specifically, the current storagemodule 214 may estimate the current storage 276 of the SCR catalyst 124based on the target supply rate, the NOx conversion efficiency 284,and/or one or more other suitable parameters.

The conversion efficiency module 218 estimates the NOx conversionefficiency 284. For example only, the conversion efficiency module 218may estimate the NOx conversion efficiency 284 based on the currentstorage 276 of the SCR catalyst 124, the target supply rate, the inputNOx 158, one or more of the temperatures, the EFR 288, and/or one ormore other suitable parameters. The EFR 288 may be measured using an EFRsensor (not shown) or determined based on, for example, the MAF.

The predicted NOx output module 222 predicts the output NOx that will bemeasured by the downstream NOx sensor 150. The predicted value of theoutput NOx may be referred to as a predicted output NOx 286. For exampleonly, the predicted NOx output module 222 may determine the predictedoutput NOx 286 based on the input NOx 158, the NOx conversion efficiency284, the EFR 288, the SCR temperature 278, an amount of nitrogen dioxide290 input to the SCR catalyst 124, an amount of HC 292 stored by theparticulate filter, and/or one or more other suitable parameters.

The NO2 input module 226 estimates the amount of nitrogen dioxide 290input to the SCR catalyst 124. The NO2 input module 226 may estimate theamount of nitrogen dioxide 290 input to the SCR catalyst 124 based onthe input NOx 158 and an estimated ratio of the input NOx 158 that isnitrogen dioxide. The estimated ratio of the input NOx 158 that isnitrogen dioxide may be estimated based on the exhaust conditions andthe input NOx 158. The exhaust conditions include, for example, exhaustpressure 294, one or more of the temperatures 160, 164, and 168, the EFR288, the equivalence ratio (EQR) of the air/fuel mixture supplied to theengine 102, and/or one or more other suitable parameters.

The adaptation triggering module 240 selectively triggers theperformance of an adaptation event. The adaptation triggering module 240selectively triggers the performance of the adaptation event based onthe output NOx 166 and the predicted output NOx 286. For example only,the adaptation triggering module 240 triggers the performance of theadaptation event when the output NOx 166 is greater than the predictedoutput NOx 286.

Referring now to FIG. 3, and with continuing reference to FIG. 2, anexemplary graph 310 of the accumulated input NOx 296 versus time, anexemplary graph 320 of the current storage 276 versus time, and anexemplary graph 330 of the output NOx 166 versus time is presented.Performance of an adaptation event is triggered at approximately time340 in FIG. 3.

The dosing management module 202 disables dosing agent injection whenthe performance of the adaptation event is triggered. The dosingmanagement module 202 may disable dosing agent injection until theadaptation ending module 244 triggers an end of the adaptation event.Instead of disabling dosing agent injection, the dosing managementmodule 202 may slow dosing agent injection in various implementations.Exemplary trace 344 tracks the current storage 276 of the SCR catalyst124. The current storage 276 decreases after the adaptation event istriggered due to the disablement (or slowing) of the injection of thedosing agent.

The timer module 248 starts the timer when the adaptation triggeringmodule 240 triggers the performance of the adaptation event. The timermodule 248 may also reset the timer to a predetermined reset value, suchas zero, when the adaptation triggering module 240 triggers theperformance of the adaptation event. The timer tracks the period of timeelapsed since the performance of the adaptation event was triggered.

The performance of the adaptation event may generally be accomplished inN sequential phases. N is an integer that is greater than or equal to 2.M is a predetermined number of the N sequential phases during which theammonia will be depleted from the SCR catalyst 124, and M is equal toN−1. M is an integer that is greater than or equal to 1. For exampleonly, M may be equal to 2 and N may be equal to 3. An exemplaryadaptation event where N is equal to 3 and M is equal to 2 isillustrated in FIG. 3.

The triggering of the performance of the adaptation event may enable theaccumulation module 252. The accumulation module 252 monitors the inputNOx 158 measured by the upstream NOx sensor 142 and determines theaccumulated input NOx 296 based on the input NOx 158. The accumulatedinput NOx 296 may refer to a total amount of NOx (e.g., grams) that hasbeen input to the SCR catalyst 124 since the adaptation event wastriggered.

The accumulation module 252 may reset the accumulated input NOx 296 whenthe performance of the adaptation event is triggered by the adaptationtriggering module 240. The accumulation module 252 may reset theaccumulated input NOx 296 to a predetermined reset value, such as zero.Exemplary trace 348 tracks the accumulated input NOx 296. As timepasses, NOx is input to the SCR catalyst 124 (and is output from theengine 102) and, therefore, the accumulated input NOx 296 increases.

The adaptation ending module 244 monitors the input and output NOx 158and 166 measured by the input and output NOx sensors 142 and 150,respectively, during the adaptation event. The adaptation ending module244 selectively triggers the end of the adaptation event based on acomparison of the output NOx 166 and the input NOx 158. Morespecifically, the adaptation ending module 244 selectively triggers theend of the adaptation event when a difference between the output NOx 166and the input NOx 158 is less than a predetermined difference 297. Inother words, the adaptation ending module 244 selectively triggers theend of the adaptation event when the output NOx 166 and the input NOx158 are within a predetermined range of each other. The adaptationending module 244 may require that the difference be less than thepredetermined difference 297 for a predetermined period beforetriggering the end of the adaptation event.

The predetermined difference (or range) 297 is variable. The differencedetermination module 270 may set the predetermined difference 297 basedon the SCR temperature 278 and the EFR 288. The difference determinationmodule 270 may additionally or alternatively set the predetermineddifference based on the engine speed 280, the engine load 282, and/orone or more other suitable parameters.

The adaptation ending module 244 monitors the timer during theadaptation event. The adaptation ending module 244 also triggers the endof the adaptation event when the timer is greater than a predeterminedmaximum period. In this manner, if the output NOx 166 and the input NOx158 are not sufficiently within the predetermined range of each otherfor the predetermined maximum period, the adaptation ending module 244still triggers the end of the adaptation event. For example only, thepredetermined maximum period may be approximately 10 minutes.

The adaptation ending module 244 also triggers the condition assessmentmodule 256 when the difference between the input and output NOx 158 and166 is less than the predetermined difference. After being triggered,the condition assessment module 256 determines a loading condition 298of the SCR catalyst 124 at the time when the performance of theadaptation event was triggered. The loading condition 298 of the SCRcatalyst 124 may be one of overloaded, underloaded, or indeterminate.

The adaptation ending module 244 may estimate a depleting amount of NOx299 based on the current storage 276 of the SCR catalyst 124 at the timewhen the adaptation event is triggered. The depleting amount of NOx 299may correspond to an estimated amount of NOx (e.g., grams) to reduce thecurrent storage 276 to zero and to deplete the SCR catalyst 124 ofammonia. Accordingly, the SCR catalyst 124 should be depleted of ammoniawhen the accumulated input NOx 296 is greater than the depleting amount299 during the adaptation event. The adaptation ending module 244 mayprovide the depleting amount 299 to the condition assessment module 256.

The condition assessment module 256 may determine the loading condition298 based on a comparison of the accumulated input NOx 296 and thedepleting amount of NOx 299. For example only, the condition assessmentmodule 256 may determine that the SCR catalyst 124 was overloaded whenthe accumulated input NOx 296 is greater than the depleting amount ofNOx 299. When the accumulated input NOx 296 is greater than thedepleting amount of NOx 299, more NOx than expected (i.e., more than thedepleting amount 299) was input to the SCR catalyst 124 before the SCRcatalyst 124 was depleted of ammonia. Thus, the condition assessmentmodule 256 may determine that the SCR catalyst 124 was overloaded whenthe accumulated input NOx 296 is greater than the depleting amount 299.Conversely, the condition assessment module 256 may determine that theSCR catalyst 124 was underloaded when the accumulated input NOx 296 isless than the depleting amount of NOx 299.

The condition assessment module 256 may notify the factor adjustmentmodule 260 of the load condition 298. The condition assessment module256 may provide the accumulated input NOx 296 and/or the depletingamount of NOx 299 to the factor adjustment module 260. The factoradjustment module 260 selectively adjusts the dosing rate adjustmentfactor 273 based on the load condition 298, the accumulated input NOx296, and/or the depleting amount 299.

More specifically, the factor adjustment module 260 selectively adjuststhe dosing rate adjustment factor 273 based on the accumulated input NOx296 and the depleting amount 299. For example only, the factoradjustment module 260 may increase the dosing rate adjustment factor 273when the accumulated input NOx 296 is less than the depleting amount 299(i.e., when the SCR catalyst 124 was underloaded). The factor adjustmentmodule 260 may decrease the dosing rate adjustment factor 273 when theaccumulated input NOx 296 is greater than the depleting amount 299(i.e., when the SCR catalyst 124 was overloaded).

The factor adjustment module 260 determines how much to adjust thedosing rate adjustment factor 273 (e.g., a magnitude of the adjustment)based on the accumulated input NOx 296 and the depleting amount 299. Forexample only, the factor adjustment module 260 may increase themagnitude of the adjustment as a difference between the accumulatedinput NOx 296 and the depleting amount 299 increases. The factoradjustment module 260 may decrease the magnitude of the adjustment asthe difference decreases. In this manner, the adjustment of the dosingrate adjustment factor 273 is made to correlate to how overloaded orunderloaded the SCR catalyst 124 was when the adaptation event wastriggered. The factor adjustment module 260 may also determine themagnitude of the adjustment based on one or more other parameters. Forexample only, the factor adjustment module 260 may determine themagnitude of the adjustment based on the (previous) value of the dosingrate adjustment factor 273 and/or the proximity of the dosing rateadjustment factor 273 to maximum and minimum values of the dosing rateadjustment factor 273.

The factor adjustment module 260 provides the dosing rate adjustmentfactor 273 to the dosing management module 202. The dosing managementmodule 202 enables dosing agent injection when the end of the adaptationevent is triggered. The dosing management module 202 determines thetarget dosing rate 272, adjusts the target dosing rate 272 based on the(adjusted) dosing rate adjustment factor 273, and provides the targetdosing rate 272 to the injector control module 206. The current storagemodule 214 resets the current storage 276 to a predetermined resetvalue, such as zero, when the end of the adaptation event is triggered.Because the end of the adaptation event is triggered once ammonia isknown to have been depleted from the SCR catalyst 124 (as indicated bythe convergence of the input and output NOx 158 166), the resetting ofthe current storage 276 to the predetermined reset value when the end ofthe adaptation is triggered ensures that the current storage 276 startsfrom an accurate starting value.

Referring now to FIG. 4A, an exemplary graph of NOx as a function oftime for when the SCR catalyst 124 is underloaded is presented.Performance of the adaptation event is triggered at approximately time402. Exemplary trace 404 tracks the input NOx 158 measured by theupstream NOx sensor 142, and exemplary trace 408 tracks the output NOx166 measured by the downstream NOx sensor 150. The exemplary graph ofFIG. 4A is illustrative of instances where the adaptation event is endedwhen the N-th phase (N is equal to 3 in FIG. 4A) is completed. Forexample only, the adaptation event ends in FIG. 4A at approximately time412.

Referring now to FIG. 4B, another exemplary graph of NOx as a functionof time for when the SCR catalyst 124 is underloaded is presented.Performance of the adaptation event is triggered at approximately time402. Exemplary trace 454 tracks the input NOx 158 measured by theupstream NOx sensor 142, and exemplary trace 458 tracks the output NOx166 measured by the downstream NOx sensor 150. As described above, theadaptation ending module 244 of the present disclosure selectivelytriggers the end of the adaptation event when the difference between theinput and output NOx 158 and 166 is less than the predetermineddifference 297. The adaptation ending module 244 of the presentdisclosure selectively triggers the end of the adaptation eventregardless of the phase of the adaptation event.

In this manner, if the SCR catalyst 124 is underloaded when theperformance of the adaptation event is triggered, the adaptation endingmodule 244 may trigger the end of the adaptation event before the N-thphase would otherwise be completed. For example only, the adaptationending module 244 may selectively trigger the end of the adaptationevent at approximately time 462, when the difference between the inputNOx 158 and the output NOx 166 is less than the predetermineddifference.

Referring now to FIG. 5A, an exemplary graph of NOx as a function oftime for when the SCR catalyst 124 is overloaded is presented.Performance of the adaptation event is triggered at approximately time502. Exemplary trace 504 tracks the input NOx 158 measured by theupstream NOx sensor 142, and exemplary trace 508 tracks the output NOx166 measured by the downstream NOx sensor 150. The exemplary graph ofFIG. 5A is illustrative of instances where the adaptation event is endedwhen the N-th phase (N is equal to 3 in FIG. 5A) is completed. Forexample only, the adaptation event ends in FIG. 5A at approximately time512.

Referring now to FIG. 5B, another exemplary graph of NOx as a functionof time for when the SCR catalyst 124 is overloaded is presented.Performance of the adaptation event is triggered at approximately time502. Exemplary trace 554 tracks the input NOx 158 measured by theupstream NOx sensor 142, and exemplary trace 558 tracks the output NOx166 measured by the downstream NOx sensor 150. As described above, theadaptation ending module 244 of the present disclosure selectivelytriggers the end of the adaptation event when the difference between theinput and output NOx 158 and 166 is less than the predetermineddifference 297. The adaptation ending module 244 of the presentdisclosure selectively triggers the end of the adaptation eventregardless of the phase of the adaptation event.

In this manner, if the SCR catalyst 124 is overloaded when theperformance of the adaptation event is triggered, the adaptation endingmodule 244 may trigger the end of the adaptation event after the N-thphase would otherwise be completed. For example only, the adaptationending module 244 may selectively trigger the end of the adaptationevent at approximately time 562, when the difference between the inputNOx 158 and the output NOx 166 is less than the predetermined difference297. However, the convergence of the input and output NOx 158 and 166,indicates that the SCR catalyst 124 is depleted of ammonia. Therefore,the current storage 276 of the SCR catalyst 124 can be accurately resetfor after the end of the adaptation event.

Referring now to FIG. 6, a flowchart depicting an exemplary method 600of performing an adaptation event is presented. Control begins at 602where control determines the predicted output NOx 286. Controldetermines whether the output NOx 166 measured by the downstream NOxsensor 150 is greater than the predicted output NOx 286 at 606. If true,control may continue with 610; if false, control may return to 602.

At 610, control may trigger an adaptation event, disable dosing agentinjection, and start a timer. Control determines the depleting amount ofNOx 299 at 614. Control may determine the depleting amount of NOx 299based on the current storage 276. Control determines the accumulatedinput NOx 296 at 618. Control determines the predetermined difference297 at 622. Control may determine the predetermined difference 297 basedon, for example, the SCR temperature 278 and the EFR 288. Additionallyor alternatively, control may determine the predetermined differencebased on the engine speed 280, the engine load 282, and/or one or moreother suitable parameters.

Control monitors the input and output NOx 158 and 166 measured by theupstream and downstream NOx sensors 142 and 150, respectively, anddetermines whether the difference between the input and output NOx 158and 166 is less than the predetermined difference 297 at 626. If false,control continues with 630; if true, control transfers to 634. 634 isdiscussed further below.

Control determines whether the timer is greater than the predeterminedmaximum period at 630. If true, control transfers to 634; if false,control returns to 618. In this manner, control continues with 634 whenthe timer is greater than the predetermined maximum period (at 630) orwhen the difference is less than the predetermined difference (at 626).For example only, the predetermined maximum period may be approximately10 minutes.

At 634, control triggers the end of the adaptation event. Control setsthe current storage 276 of the SCR catalyst 124 equal to zero at 638.Control determines the adjustment amount for the dosing rate adjustmentfactor 273 at 642. In other words, control determines whether toincrease or decrease the dosing rate adjustment factor 273 and controldetermines how much the dosing rate adjustment factor 273 should beincreased or decreased at 642. For example only, control may increaseand decrease the dosing rate adjustment factor 273 when the accumulatedinput NOx 296 is less than and greater than the depleting amount 299,respectively. The magnitude of the increase or decrease may increase asthe difference between the accumulated input NOx 296 and the depletingamount 299 increases.

Control adjusts the dosing rate adjustment factor 273 at 646. Controlmay then end. Control re-enables dosing agent injection after the end ofthe adaptation event is triggered, and control adjusts the target dosingrate 272 based on the dosing rate adjustment factor 273. In this manner,the rate of dosing agent injection after the adaptation event isadjusted to minimize future overloading or underloading of the SCRcatalyst 124.

The broad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, the specification, and the following claims.

1. A dosing control system for a vehicle, comprising: a current storagemodule that estimates an amount of ammonia stored by a selectivecatalytic reduction (SCR) catalyst; an adaptation triggering module thattriggers a reduction of the amount of ammonia stored by the SCR catalystto zero when a first amount of nitrogen oxides (NOx) measured by a firstNOx sensor located downstream of the SCR catalyst is greater than apredicted value of the first amount of NOx; and an adaptation endingmodule that selectively ends the reduction and enables injection ofdosing agent based on a comparison of the first amount of NOx with asecond amount of NOx upstream of the SCR catalyst.
 2. The dosing controlsystem of claim 1 wherein the adaptation ending module selectively endsthe reduction and enables injection of dosing agent based on adifference between the first and second amounts of NOx.
 3. The dosingcontrol system of claim 1 wherein the adaptation ending moduleselectively ends the reduction and enables injection of dosing agentwhen a difference between the first and second amounts of NOx is lessthan a predetermined difference.
 4. The dosing control system of claim 3wherein the adaptation ending module selectively ends the reduction andenables injection of dosing agent when the difference is less than thepredetermined difference for a predetermined period.
 5. The dosingcontrol system of claim 3 further comprising a difference determinationmodule that determines the predetermined difference based on atemperature of the SCR catalyst and an exhaust flow rate.
 6. The dosingcontrol system of claim 3 further comprising a difference determinationmodule that determines the predetermined difference based on an enginespeed and an engine load.
 7. The dosing control system of claim 3further comprising: an accumulation module that determines a totalamount of NOx input to the SCR catalyst during the reduction; and acondition assessment module that, when the difference is less than thepredetermined difference, selectively determines whether the estimatewas one of greater than and less than an actual amount of ammonia thatwas stored by the SCR catalyst based on a second comparison of the totalamount of NOx with a depleting amount of NOx determined based on theestimate.
 8. The dosing control system of claim 7 further comprising: afactor adjustment module that one of increases and decreases a dosingrate adjustment factor when the estimate was less than and greater thanthe actual amount, respectively; and a dosing management module that,after the adaptation ending module ends the reduction and enables theinjection of dosing agent, adjusts a target dosing rate based on thedosing rate adjustment factor and controls the injection of dosing agentto achieve the target dosing rate.
 9. The dosing control system of claim8 wherein the factor adjustment module determines a magnitude based onthe total amount of NOx and the depleting amount of NOx and one ofincreases and decreases the dosing rate adjustment factor based on themagnitude.
 10. The dosing control system of claim 8 wherein the factoradjustment module determines a magnitude based on a difference betweenthe total amount of NOx and the depleting amount of NOx and one ofincreases and decreases the dosing rate adjustment factor based on themagnitude.
 11. A dosing control system for a vehicle, comprising: anadaptation triggering module that triggers an adaptation event when afirst amount of nitrogen oxides (NOx) measured by a first NOx sensorlocated downstream of a selective catalytic reduction (SCR) catalyst isgreater than a predicted value of the first amount of NOx; a dosingmanagement module that disables injection of dosing agent during theadaptation event; and an adaptation ending module that selectively endsthe adaptation event based on a comparison of the first amount of NOxwith a second amount of NOx measured by a second NOx sensor locatedupstream of the SCR catalyst.
 12. A dosing control method for a vehicle,comprising: estimating an amount of ammonia stored by a selectivecatalytic reduction (SCR) catalyst; triggering a reduction of the amountof ammonia stored by the SCR catalyst to zero when a first amount ofnitrogen oxides (NOx) measured by a first NOx sensor located downstreamof the SCR catalyst is greater than a predicted value of the firstamount of NOx; and selectively ending the reduction and enablinginjection of dosing agent based on a comparison of the first amount ofNOx with a second amount of NOx upstream of the SCR catalyst.
 13. Thedosing control method of claim 12 further comprising selectively endingthe reduction and enabling injection of dosing agent based on adifference between the first and second amounts of NOx.
 14. The dosingcontrol method of claim 12 further comprising selectively ending thereduction and enabling injection of dosing agent when a differencebetween the first and second amounts of NOx is less than a predetermineddifference.
 15. The dosing control method of claim 14 further comprisingselectively ending the reduction and enabling injection of dosing agentwhen the difference is less than the predetermined difference for apredetermined period.
 16. The dosing control method of claim 14 furthercomprising determining the predetermined difference based on atemperature of the SCR catalyst and an exhaust flow rate.
 17. The dosingcontrol method of claim 14 further comprising determining thepredetermined difference based on an engine speed and an engine load.18. The dosing control method of claim 14 further comprising:determining a total amount of NOx input to the SCR catalyst during thereduction; and, when the difference is less than the predetermineddifference, selectively determining whether the estimate was one ofgreater than and less than an actual amount of ammonia that was storedby the SCR catalyst based on a second comparison of the total amount ofNOx with a depleting amount of NOx determined based on the estimate. 19.The dosing control method of claim 18 further comprising: one ofincreasing and decreasing a dosing rate adjustment factor when theestimate was less than and greater than the actual amount, respectively;after the adaptation ending module ends the reduction and enables theinjection of dosing agent, adjusting a target dosing rate based on thedosing rate adjustment factor; and controlling the injection of dosingagent to achieve the target dosing rate.
 20. The dosing control methodof claim 19 further comprising determining a magnitude based adifference between the total amount of NOx and the depleting amount ofNOx and one of increases and decreases the dosing rate adjustment factorbased on the magnitude.